1. Field of the Invention
This invention relates to new grease compositions; and, more particularly, to improved, low-wear grease for heavy duty, high temperature applications, such as for journal bearings on bits drilling into hot subterranean formations.
2. Description of the Prior Art
Complex-thickened greases are well known in the art. For example, an excellent discussion is contained in the ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY, KIRK-Othmer, Second Edition, A. Standen, Editor, Interscience Publishers, John Wiley & Sons, Inc., New York, N.Y., 1967, pages 582-587. Also, it is known to employ certain complexes; such as, the calcium-acetate-containing complexes and the lithium-hydroxy-stearate-containing complexes; to provide high temperature stability and maintain lubrication properties at the high temperatures to which the greases may be subjected.
Lubricating a drill bit drilling in hot (frequently above 300.degree.F) subterranean formations is one of the most severe and demanding set of conditions ever posed for a lubricant. The drilling takes place in an abrasive atmosphere of drilling mud and rock particles thousands of feet from the engineer or supervisor, who does not have benefit of oil pressure gauges or temperature sensors at the surfaces to be lubricated. The lubricant should have properties that enable flow through passageways to the surfaces to be lubricated and that prevent solid lubricant particles from settling out.
The best available lubricants heretofore have not satisfactorily minimized wear under the heavy load conditions encountered by earth boring drill bits having friction bearings.
The prior art shows solid extreme pressure (EP) additives have been employed to attempt to enhance the lubrication properties of oils and greases. For example, molybdenum disulfide has been used in a wide variety of lubricants, as noted in U.S. Pat. Nos. 3,062,741, 3,170,878, 3,281,355 and 3,384,582. The prior art has taught, however, that the molybdenum disulfide should comprise fine particles having an average diameter less than 10 microns and some prefer less than 2 microns.
Also, it is known to include metallic oxides like zinc oxide in other lubrication oils. Moreover, U.S. Pat. No. 2,736,700 describes the use of molybdenum disulfide and a metallic oxide, such as fumed lead oxide and zinc oxide in a ratio of 2 parts molybdenum disulfide to 1 part metallic oxide, in a paint-on composition, or bonded lubricant, containing a lacquer drying agent. The bonded lubricant is described for drawing tough metals, such as uranium, thorium, zinc and titanium. Such bonded lubricants are inadequate and could not be employed in the low-wear, heavily loaded applications for which this invention was engineered.
Insofar as I am aware, the prior art has not provided a heavy duty lubricant employing a hydrocarbonaceous grease that is calcium acetate complex thickened for temperature stability and that has the superior lubricating properties of this invention; particularly, that could be employed in the application of lubricating journal bearings in bits drilling in an abrasive atmosphere thousands of feet from the engineer or supervisor; or under conditions that are similarly severe and demanding of the grease.